设计模式--迭代器模式

提供一种方法顺序访问一个聚合对象中各个元素，而又不暴露该对象的内部表示。

当你需要访问一个聚集对象，而且不管这些对象是什么都需要遍历的时候，就应该考虑用迭代器模式。

//定义一个迭代器抽象类

//迭代器抽象类
abstract class Iterator
{
//用于定义得到开始对象，得到下一个对象、判断是否到结尾、当前对象等抽象方法，统一接口。
public abstract object First();
public abstract object Next();
public abstract bool IsDone();
public abstract object CurrentItem();
}

//聚集抽象类
abstract class Aggregate
{
//创建迭代器
public abstract Iterator CreateIterrator();
}

class ConcreteAggregate : Aggregate
{
//声明一个IList泛型变量，用于存放聚合对象。
IList<object> items = new List<object>();
public override Iterator CreateIterrator()
{
return new ConcreteIterator(this);
}
//返回聚集总个数
public int Count { get { return items.Count; } }
//声明一个索引器
public object this[int index]
{
get { return items[index]; }
set { items.Insert(index, value); }
}

}

//具体迭代器类，继承Iterator
class ConcreteIterator : Iterator
{
ConcreteAggregate aggregate;
int current = 0;
public ConcreteIterator(ConcreteAggregate aggregate)
{
this.aggregate = aggregate;
}

public override object CurrentItem()
{
return aggregate[current];
}

public override object First()
{
return aggregate[0];
}

public override bool IsDone()
{
return current >= aggregate.Count ? true : false;
}

public override object Next()
{
object obj = null;
current++;
if(current<aggregate.Count)
{
obj = aggregate[current];
}
return obj;

}
}

调用：

ConcreteAggregate aggres = new ConcreteAggregate();
aggres[0] = "dd";
aggres[1] = "aa";
aggres[2] = "cc";

Iterator it = new ConcreteIterator(aggres);
while (!it.IsDone())
{
Console.WriteLine(it.CurrentItem());
it.Next();
}

倒序

改写或添加具体迭代器类

class ConcreteIteratorDesc : Iterator
{
ConcreteAggregate aggregate;
int current = 0;

public ConcreteIteratorDesc(ConcreteAggregate aggre)
{
this.aggregate = aggre;
this.current = aggre.Count-1;
}

public override object CurrentItem()
{
return aggregate[current];
}

public override object First()
{
return aggregate[this.aggregate.Count-1];
}

public override bool IsDone()
{
return current < 0 ? true : false;
}

public override object Next()
{
object obj = null;
current--;
if (current >= 0)
{
obj = aggregate[current];
}
return obj;
}

}

调用：

改写下Iterator的实例为ConcreteIteratorDesc就可以了

Iterator it = new ConcreteIterator(aggres);